1. Field of the Invention
This invention relates to crosslinked copolymers of maleic anhydride (MAN) and methyl vinyl ether (MVE), and, more particularly, to a process of making such crosslinked copolymers in high yield in the form of fine white powders, which, upon aqueous hydrolysis, can form clear gels.
2. Description of the Prior Art
Goertz, in U.S. Pat. No. 4,952,558, described a method of making copolymers of ethylenically unsaturated dicarboxylic anhydrides, e.g. maleic anhydride (MAN) and alkyl vinyl ethers, e.g. methyl vinyl ether (MVE). The Goertz process consisted of precharging solid MAN in isopropyl acetate, metering in the MVE and initiator, heating to boiling and filtering the resultant slurry. The product obtained was coarse powders of uncrosslinked copolymers. However, no examples were presented therein for making crosslinked copolymers.
Tazi, in U.S. Pat. No. 5,034,488, described a method of making crosslinked copolymers of MAN and MVE in a solvent system of cyclohexane and ethyl acetate.
Accordingly, an object of the invention is to provide a process for making crosslinked copolymers of maleic anhydride and methyl vinyl ether in high yield in the form of fine white powders.
Another object herein is to provide such crosslinked copolymer powders which can be readily hydrolyzed to form clear aqueous gels.
A feature of the invention is the provision of a process for making crosslinked copolymer powders of MAN and MVE, wherein molten MAN monomer is continuously fed into the precharged mixture of MVE and a suitable crosslinker.
Another feature herein is the provision of a filterable suspension of a crosslinked copolymer of MAN and MVE, at about a 30-50% solids level, from which fine white powders of the copolymer can be readily obtained.